This invention relates to digital information storage systems of the type accessible by a central processing unit.
Digital information storage facilities are known which are designed to store large quantities of information in digital form and which are normally accessible by a general purpose digital computer. In such systems, the digital information is typically stored on magnetic record media, such as disk packs or magnetic tapes and forms a data base of user information, such as inventories, payroll and accounting records, weather data, seismic data and the like. The storage facility is normally associated to a general purpose digital computer capable of extracting information from the record media, processing the extracted information and returning processed information to the record media.
In the past, all significant data processing functions have been performed in the host digital computer, and the information storage facility has functioned merely as a slave to the host computer or at best as a simple fixed location single key search, and has been provided with a functional capability of merely transferring information thereto. In a typical installation, the host computer is provided with a resident program for specifying the manner in which information is to be processed and, once operational, one or more application programs are performed step by step in the host computer until a step in a given program is reached which requires information from the storage facility. Thereafter, further activity in the specific program is terminated and the host computer transmits a request to the information storage facility to retrieve a first index block. That block of information is located and transferred to buffer storage in the host computer after which the computer searches for a reference, commonly termed a pointer. Once the pointer has been located, another index block is requested by the host computer and transferred from the storage facility to the host computer buffer storage, after which the second index block is searched for an additional pointer. This process continues for several iterations until the particular record block has been located in the storage facility and transferred to the host computer, whereupon the application program may be resumed. The application program then must extract the individual data item of interest. Each transfer of information between the host computer and the storage facility requires a high speed data path in order for the process to operate with some degree of efficiency, which in turn requires that the host computer be in close physical proximity to the information storage facility. This requirement of close physical proximity is inconvenient in some applications and totally undesirable in others.
An even greater disadvantage to known systems of this type is the fact that a large percentage of the functional capability of the host compouter is diverted from the execution of the application program, and thus wasted, due to the relatively large amount of computer time spent in obtaining a file, record or item from the information storage facility. As the size or use of the data base expands, the amount of host computer time spent on index retrieval and searching expands accordingly, which renders known systems of this type even more inefficient. While some information storage facilities have been designed for use with more than one host computer, such systems have not remedied the disadvantages noted above.